1- Roughly chop the graham crackers and chocolate bar. Tear the mini marshmallows in half to help them melt just right in the dough.

2- Whisk together the flour, salt, baking powder, baking soda, and cornstarch in a bowl. Set this aside so it’s ready to go.

3- Using a mixer, beat the butter and sugars until they’re creamy, which takes about 2 minutes. Then beat in the egg and vanilla until everything is combined, scraping down the bowl as needed.

4- Gradually add the flour mixture to the butter mixture on low speed, mixing just until it’s all combined. Don’t overdo it here to keep the cookies tender.

5- Reserve a handful of the torn marshmallows. Add the remaining marshmallows, chocolate chips, and chopped graham crackers to the dough. Mix on low speed just until incorporated.

6- Refrigerate the dough for at least 1 hour. This step helps the flavors blend and prevents the cookies from spreading too much.

7- Preheat your oven to 350°F (175°C). Portion the dough into balls, about 2 tablespoons each, and place them 2 inches apart on parchment-lined baking sheets.

8- Bake for 8 minutes. Take them out and top each cookie with the reserved marshmallows and pieces of the chopped chocolate bar. Pop them back in the oven for 2-3 more minutes.

9- If the marshmallows spread too much, use a round cookie cutter or knife to gently push the edges back toward the center right away.

10- Let the cookies cool completely on the baking sheet before moving them. This makes them easier to handle and lets them firm up.